A Kurdish militant group on Friday claimed responsibility for a car-bomb attack in Istanbul this week that killed 11 people, saying it was just the beginning of a war.

In a statement posted online, the Kurdistan Freedom Falcons also warned tourists that Turkey was no longer secure for them.

"You are not our targets but Turkey is no longer safe for you," it read. "We have just started the war."

The Kurdistan Freedom Falcons is considered an offshoot of the Kurdistan Workers' Party, or PKK, and has carried out several attacks in the past.

It denounced the ruling Justice and Development Party, which was founded by President Recep Tayyip Erdogan, for its "wild war" against Kurds.

Turkey's southeast plunged into violence last summer when a 2½-year fragile truce between the state and Kurdish rebels collapsed.

The rush hour car-bomb attack on Tuesday morning targeted a police vehicle in Istanbul and injured 36 people in addition to those killed.

Istanbul's bombing was followed on Wednesday by a suicide attack in the southeastern town of Midyat that killed three police officers and three civilians.

On Thursday, The PKK said the Midyat attack was carried out by one of its "comrades," code name Dirok Amed.

The authorities were quick to report they suspected Kurdish militants in both cases. The claims of responsibility confirmed those suspicions.

The Kurdistan Freedom Falcons, also known as TAK, was also behind two deadly suicide bombings this year in Ankara, the capital.

The PKK routinely attacks military and police targets in the southeast, where large-scale security operations to flush out Kurdish rebels have left hundreds dead, displaced entire communities and done extensive damage to urban infrastructure.

The PKK, labeled a terror organization by Turkey and its allies, is fighting for autonomy for Turkey's Kurds in the southeast. The decades-long conflict has claimed 40,000 lives.

In the past year, Turkey has been hit by a series of bombings — including two in Istanbul targeting tourists — which the authorities have blamed on the Islamic State group. The attacks have increased in scale and frequency, scaring off tourists and hurting the economy, which relies heavily on tourism revenues.

In a bid to curb such attacks, the government is mulling measures to keep tabs on the sale of materials made to use improvised explosive devices, such as gas canisters commonly used for cooking, officials said Friday.

The announcement came a day after the agriculture minister said the government has temporarily suspended the sale of fertilizers containing nitrate that can be used to make explosives.